In recent years, due to advances in image compression and encoding techniques such as the MPEG scheme, it is now common to convert an image signal into a digital form for handling. For example, in the field of television broadcasting, while digital broadcasting using BS (Broadcasting Satellite) has already been in use, recently, digital terrestrial broadcasting has also been launched. These types of digital broadcasting use the MPEG scheme as the compression and encoding scheme to provide, in addition to conventional SD (Standard Definition) images, HD (High Definition) images with higher resolution.
On the other hand, there has been a rapid proliferation of digital video recorders which record video signals as digital data onto an optical disk or an HDD (Hard Disk Drive). In recent years, in particular, much attention is being given to a Blu-ray Disc as a portable optical disk with higher capacity. Video recorders using such a Blu-ray Disc are already on the market. A Blur-ray disc is capable of recording HD images compressed and encoded in the MPEG scheme for about two hours.
In digital video decoders, after an MPEG stream in the TS format compressed and encoded in the MEG scheme is received through broadcasting, the MPEG stream is recorded onto a recording medium as it is without any alterations, thus making it possible to retain the image quality of the original image. The use of an HDD or Blur-ray disc, in particular, allows the recording of not only an SD image but also an HD image to be performed without causing a degradation in image quality. Further, recording the received data as it is also proves advantageous from the viewpoint of simplifying the configuration of the apparatus.
In the MPEG scheme, synchronous reproduction of video is realized by referring to reproduction time information described in the data stream, and the time of a clock outputted by a reproducing apparatus. Specifically, for each individual access unit of video and audio data, a PTS (Presentation Time Stamp) as reproduction/output time management information and, as required, a DTS (Decoding Time Stamp) as decoding time management information are described. In addition, a PCR (Program Clock Reference) and an SCR (System Clock Reference) are described as the reference values for these time management information. By referring to the PCR and SCR values, the reproducing apparatus causes the reference time intended on the encoder side to be reproduced by means of a synchronization signal called an STC (System Time Clock) inside the decoder, and controls, on the basis of the value of this STC and the PTS and DTS, the decoding and reproduction/output timings of the corresponding access unit.
As an example of conventional data transmission systems using a TS (Transport Stream) of the MPEG scheme as described above, there is a system including a multiplexer that calculates a PCR correction value on the basis of the arrival and expected output times of TS packets from a plurality of encoders based on a reference clock, thereby making it possible to correct the PCR without receiving a reference clock from the encoders (see, for example, Japanese Unexamined Patent Application Publication No. 9-321727 (paragraphs [0016] to [0030] and FIG. 1)).